1. Field of the Invention
The present invention relates a tubular structure which comprises a plurality of tubular sections connected in a vertical direction and a wind turbine generator, in particular, a tubular structure and a wind turbine generator in which a plurality of tubular sections are joined by means of a splice plate and a fastening member.
2. Description of the Related Art
It has been a well-known technique to form a tubular structure extending in a vertical direction having an object to be supported on top thereof in order to support the object on a high place. For instance, a wind turbine generator comprises a rotor head having a blade mounted thereon, a nacelle housing a generator to which the rotation of the blade is inputted via the rotor head and a tower constituted of a tubular structure for supporting the nacelle rotatably.
The tower is generally made of steel material. The most common type is a monopole type, which is one supporting structure for supporting the blades, the rotor head and the nacelle. In a large-sized wind turbine generator, the height of the tower can range approximately from tens to hundreds meters, and thus from the aspect of production and transportation thereof, the tower is divided into several tubular sections and the plurality of tubular sections are joined with one another to form a tower.
During the process of constructing the wind turbine generator, the plurality of tubular parts are separately transported and joined at a construction site to assemble a tower. As a conventional coupling structure of the tower, a flange projects toward an inner side of the tubular section and the abutting flanges of the adjacent tubular sections are fixed to each other by a high-strength bolt so as to join the adjacent tubular sections.
However, this joining method is a tension joint which uses the high-strength bolt to join the flanges. This requires the flanges to be produced precisely and often uses forging material for the flange, whose material cost per unit is more expensive than rolled steel. Further, When the wind turbine generator using tension joint for connection between tubular sections is assembled at construction site, the preliminary fastening of the bolts is performed after the tubular sections are installed and then the final fastening of the bolts are necessary after installing the blades, the rotor head and the nacelle thereon. Furthermore, to take measure against loosening of the bolts during the operation of the wind turbine generator, a periodic inspection and retightening of the bolts are necessary, resulting in complicating the work.
In view of the above issues, a flangeless tower is proposed. In the flangeless tower, tubular sections are connected without using a flange and the tubular sections are joined by friction joint with use of splice plates. For instance, Patent Document 1 (US2008/0041009A1) proposes the structure wherein a plurality of splice plates, i.e. finger plates are arranged at an even interval on an inner face and an outer face of the adjacent tubular sections and the tubular sections and the splice plates are fastened by bolts and nuts so as to join the adjacent tubular sections. Patent Document 2 (JP2010-077965A) also discloses the structure wherein the arrangement of splice plates is specifically defined.